Beneficiating method and apparatus therefor



March 1956 c. c. COOK, JR

BENEFICIATING METHOD AND APPARATUS THEREFOR Filed March 50 AT T HRNE Y United States Patent BENEFICIATING METHOD AND APPARATUS THEREFOR Charles C. Cook, Jr., Lakeland, Fla., assignorto International Minerals & Chemical Qorporation, a corpo- This invention relates to the concentration of minerals of a dielectric or nonconducting nature. More particularly, it relates to electrostatic separation of multicomponent materials of fine particle size. Still more particularly, it relates to apparatus for charging fines from ore sizing operations. v

1 Flotation processes of phosphate rock. have been lim-. ited in the particle size. of material which can be successfully handled. Phosphate ores of less than 200. mesh size have generally been removed in hydroseparators and lost in a discarded material referred to under the generic term slimies.

Electrostatic beneficiation processes heretofore in use likewise have been limited as to. the particle size and material which could be successfully efiiciently separated. Particle size for materials being fed to electrostatic sepa: rato'rs generally falls in the range, between 14, and 200 mesh. For better separationsthe. material to be electrostaticallyw beneficiated has been screened into, a, material ofi a much narrower range, the particle-size rangeha-ving a. spread of only about 40 mesh sizes;

The electrostatic methods have failed; when attemptswere made to beneficiate fines in the normal manner of passingthem, while hot, over. a metal which readily gives up areal-ans; because only a small; percentage of the fines: ever make contact with the metal if, commercially feast; ible v volumesof fines are delivered to the contact surface. Thenormal operations have. also failed because fine par-- tiele's, tend to coat thecontact surface insulating the metal: from flowing powder material, Additional, interference with separations arises from flocks of charged and. uncharged particles which, are not. dispersed; during the travelthr ough an eleetrostaticfield.

It. isanobject of the. present invention, to recover maa terial-smaller. than 200 mesh, thus overcoming. one of; the important disadvantages: encountered; in prion art processes.

Itisa. further object to provide an.,electrostatic benea fieiation method-for fine formerly-discarded materials;

It isa further object tolprovid'e anelectrostaticbeneficiation; method for recovery, of: higher. percenta'gesi ofz phosphatic material from phosphate ores.

It; is, still a; further. objectto provide an. electrostatic beneficiation method for recovery ofrphosphatic' material formerlydiscardedin sq-ealled: slimes,

It. is a still further ObjCtl to provide: apparatus for efiicientseparationof small'particl'e si'ze ore: material.

It is, a. still further. object of. theiinvention to provideapparatus for eifectively inducing small particlesito'v ac ceptanelectric. charge.

It is. astill furtherobject. to provide apparatuswherein flocculationof small particles which heretofore interferedwith separations i'szprevented. I

These and other objects will be apparent upona-fuller understanding. of; the novel; process; and: apparatus as hereinaftendescribed in detaih.

It. has; now been; discovered" that quartz. orsili'cona dioxidercontaining. material of? small zmeslnsizesg; suelrz as:-

mechanically produced phosphate fines, for instance the fines separated after rock grinding and corresponding products encountered in the processing of other. nonmetallic minerals, can be efiectively beneficiated and commercially useful concentrates obtained thereby.

The new and novel method comprises suspending fine particle size multicomponent ore in an air stream, inducing the suspended material to accept an electric charge by passing through and in contact with a donor metal network or fine mesh permeable to material of the largest particle size being suspended, and subjecting the charged material to one or more. electrostatic fields of relatively low impressed difiference of potentiaL- Any suitable dry inert gas,- such as combustion gases, nitrogen, carbon dioxide, etc., may be used in place of air. 7

In one embodiment of this method for beneficiating fines, the lines are accumulated as, a result of air-sizing ground ore. These dry fines are. of a material generally less than 200 mesh in size, very efiective. beneficiation being accomplished with material of a particle size in the range between about 200 mesh and about 400 mesh. the fine material is not in dry form, the material is dried by suitable means, such as an electric. oven, rotary kiln, and the like, at a temperature in the. range of between about F. and about 500 F. Phosphate ore generally is dried in, the, preferred range of between aboutv 250 F. and about 325 F.

The dry powdery material, is suspended in air, or other inert dry gas, while, hot, by controlled discharge as by metering the solids into the gas outlet stream from a fan, turboblower compressors, and thelike, or equivalent means for introducing the. powder into. a movinggas stream..

In, order to escapefrom the blower, the powder suspension, is required to pass. through, a grounded fine mesh screen, 01', grid. This, grid is adapted to, be a grounded donor element of low work function, i; e., a metal that readily transfers electronsto the ore. material. Graphite is an excellent donor element material producing a high relative charge on phosphate ore powder. Zinc. and galvanized iron likewise. produce a strong relativecharge. Other seful materials for char-ging ore' material arecop er,.ir on, aluminum, aluminum alloys, and, the like; and, metalfcoated conductors, and. nonconductors having a surface of, coppenzinc, tin, and; the like.

After passing through the, screen, suspensions.- of charged powder are. directed to pass; through an electrostatic field. The ditfer'encein potential impressed upon; the. electrodes is generally in the range of 20,000; to; 25 0,000 volts, preferably in the range: of 35',000-to= 60,000..- volts, at afield-strength of. about.-2-;000 to about 12,000? voltsper, inehofi distance separating the electrodes; The. method of separating. ore into componentswill be more. fully" understood from the following; description; incon? junction with the drawing of. apparatus suitable. for. carny-' ing out themethodl in which: I i

Fi ure. l isa side elevational View of an electrostatic:v separation, unit? utilizing; an air blower,

Fjgur z isa front elevational view'of: the apparatusof: Figjnrel'.

Figure 3- is a schematic side elevational view of; an alternative electrostatic separation unit.

Briefly, the charging unit: comprises conduit means adapted to. direct gaslfiow, powder inlet means-:for.. said conduit, gas inlet,- means for said conduit, and aqdonor screen of fine mesh permeable to said powderpositionedi across said conduit so that powder and gas must pass therethrough, said grid being" grounded to the earth by an; electrical conductor. V a

In, a preferreda embodimentlof the-inventiomtheelectrostatic; separation; unit comprises: at''- least" one pair-of electrodes andzablower or:fair-having a copper" screen covering the outlet conduit of the blower which is permeable to the powder and grounded to the earth. The particles of the hot powder in suspension striking the screen are selectively charged. Powder and air passing through the screen is directed to pass between the set of electrodes whose material of construction is conductor metals, such as copper, iron, aluminum, aluminum alloys, and the like; metal-coated conductors and nonconductors surfaced with copper, zinc, aluminum, tin, and the like.

In a second embodiment, powder is entrained by a high-speed jet of air or other suitable gas. The apparatus comprises at least one pair of electrodes, a substantially airtight chamber, an air jet nozzle within said chamber, an air conduit connected to said nozzle, a tubular member positioned to receive air from the nozzle longitudinally thereof and extending outside said chamber to direct powder between said electrodes. The conduit is provided either at the end or intermediate the ends thereof with an electron donor screen grounded to the earth. This donor screen generally is of a mesh size generally in the range of 6 to 100 mesh. The outlet from the conduit is arranged to direct the issuing powder suspension between the electrodes of an electrostatic separation unit.

The invention will be more fully understood by reference to the drawings.

Referring to Figures 1 and 2, the numeral 10 indicates a blower provided internally with suitable vanes. Blower 10 is provided with an air inlet 11 and a powder inlet 12. Powder is delivered to the inlet 12 by gravity feed through pipe 13 from the discharge end of screw conveyor 14 provided with a helical screw 15. Blower 10 is provided with an outlet 16 covered at the end by copper screen 17 grounded to the earth by electrical conductor 18.

Material and air passing through screen 18 is delivered between electrodes 19 and 20. Material separated by the electrodes is recovered in suitable collection means adjacent the bottom of the electrodes, such as hoppers 21, 22, and 23. Hopper 22 is provided on opposite walls with pivot arms 24 and 25 adapted to be secured at any desired angle for altering the cut-point for the various fractions.

In Figure 3 there is diagrammatically illustrated a second embodiment of the invention. In this figure there is shown a hopper 30. Hopper is provided with a rotary seal outlet 31 adapted to feed powder to a substantially airtight chamber 32 on a semicontinuous basis. Chamber 32 is provided at the bottom with a nozzle 33 adapted for connection to a source of high pressure air by conduit 34. Adjacent the base of the nozzle 33, the nozzle unit is provided with a group of small ports 33a directed radially and adapted to aerate powder in chamber 32. Nozzle 33 discharges a jet of air into pipe 35. Pipe or conduit 35 is provided internally with screen 36 grounded to the earth by conductor 37. Conduit 35 directs powder between electrodes 38 and 39 which are connected to a suitable source of electricity in such manner that one electrode carries a high potential electrostatic charge of one sign and the other electrode carries a charge of the opposite sign. Segregated powder units are collected in hoppers 40, 41, and 42 provided with suitable hinged pivot arms 43 and 44, adapted to alter the cut-point of the various fractions.

The following example illustrates one operation of the method when treating Florida phosphate ore. Florida phosphate rock of about 60% B. P. L. was ground and screened to produce an ore fraction, 96% of which passed a 325 mesh standard Tyler screen.

Example This fine ore fraction was dried. in an electric oven at a temperature of about 300 F. Dry screened ore of about a 65% B. P. L. content was: delivered while hot to an air blower at a rate of about of a ton per hour per Concentrate Tails B. P. L. Insol. B. P. L. Insol. 76.4 1. 5 52.4 23

A middling fraction obtained requires additional proc-- essing to recover its phosphate values.

Having thus fully described and illustrated the character of the invention, what is desired to be secured and claimed by Letters Patent is:

1. A method of beneficiating fine multi-componcnt ore having a particle size in the range between about 200 mesh and about 400 mesh which have a tendency to ag glomerate, comprising suspending warm ore particles in an air stream, passing suspended solids into electron exchange relationship with and through a donor screen whereby the particles are induced selectively to accept an electrical charge and any agglomerated particles are thus reduced in size, the passage of these suspended solids being limited to particles of a size capable of escaping through a donor screen of mesh size in the range between about 6 mesh and about 100 mesh and passing the charged particles through at least one electrostatic field.

2. A method of beneficiating phosphate ore having a particle size in the range between about 200 mesh and about 400 mesh which have a tendency to agglomerate, comprising heating the particles to a temperature in the range of between about F. and about 500 F., suspending the solids in a moving air stream, passing suspended solids into electron exchange relationship with and through a 10 mesh donor screen whereby the particles are induced selectively to accept an electrical charge and any agglomerated particles are thus reduced in size and subjecting the charged particles to the attractive and repulsive forces of an electrostatic field having a difierence of potential impressed upon the electrodes in the range between about 35,000 volts and about 250,000 volts.

3. An electrostatic separation apparatus for material of fine particle size comprising at least one pair of electrostatic electrodes, an air blower, a conduit connected to said blower for directing air flow between electrodes, powder feed mechanism for delivery of particles to the inlet of said conduit whereby powder is entrained in air flowing through said conduit, a grid of mesh permeable to said powder positioned across said conduit so that air and powder must pass therethrough, said grid having at least an electrical conductor surface and being grounded to the earth.

4. An electrostatic separation apparatus for material of fine particle size comprising at least one pair of elcc trostatic electrodes, a chamber, powder feed mechanism for delivering powder into said chamber, an air nozzle adjacent the bottom of said chamber, a conduit positioned to receive air longitudinally from said nozzle, and having the end of said conduit extending outside said chamber and directed to position the air stream between electrodes of opposite polarity, a metal screen positioned across said conduit so that air and powder must pass theret'nrough, said screen being grounded to the earth by an electrical conductor.

5. An electrostatic separation apparatus for material of fine particle size comprising at least one pair of electrostatic electrodes, an air blower having an outlet conduit, powder feed mechanism for delivery of powder to the outlet side of said blower, a metal screen positioned across said conduit so that air and powder must pass therethrough, said screen being grounded to the earth by an electrical conductor.

6. An electrostatic separation apparatus for material of fine particle size comprising at least one pair of electrostatic electrodes, an air blower, a conduit connected to said blower for directing air flow between electrodes, powder feed mechanism for delivery of particles to the inlet of said conduit whereby powder is entrained in air flowing through said conduit, 21 grid of mesh permeable to said powder positioned across said conduit so that air and powder must pass therethrough, said grid having at least an electrical conductor surface and being grounded to the earth, and collection hoppers for separated material.

7. An electrostatic separation apparatus for material of fine particle size comprising at least one pair of electrostatic electrodes, a chamber, powder feed mechanism for delivering powder into said chamber, an air nozzle adjacent the bottom of said chamber, a conduit positioned to receive air longitudinally from said nozzle, and having the end of said conduit extending outside said chamber and directed to position the air stream between electrodes of opposite polarity, a metal screen positioned across said conduit so that air and powder must pass therethrough, said screen being grounded to the earth by an electrical conductor, and collection hoppers for separated material.

References Cited in the file of this patent UNITED STATES PATENTS Keyser et al. Jan. 20, 1942 Smith Nov. 23, 1948 OTHER REFERENCES 

1. A METHOD OF BENEFICIATING FINE MULTI-COMPONENT ORE HAVING A PARTICLE SIZE IN THE RANGE BETWEEN ABOUT 200 MESH AND ABOUT 400 MESH WHICH HAVE A TENDENCY TO AGGLOMERATE, COMPRISING SUSPENDING WARM ORE PARTICLES IN AN AIR STREAM, PASSING SUSPENDED SOLIDS INTO ELECTRON EX CHANGE RELATIONSHIP WITH AND THROUGH A DONOR SCREEN WHEREBY THE PARTICLES ARE INDUCED SELECTIVELY TO ACCEPT AN ELECTRICAL CHARGE AND ANY AGGLOMERATED PARTICLES ARE THUS REDUCED IN SIZE, THE PASSAGE OF THESE SUSPENDED SOLIDS BEING LIMITED TO PARTICLES OF A SIZE CAPABLE OF ESCAPING THROUGH A DONOR SCREEN OF MESH SIZE IN THE RANGE BETWEEN ABOUT 6 MESH AND ABOUT 100 MESH AND PASSING THE CHARGED PARTICLES THROUGH AT LEAST ONE ELECTROSTATIC FIELD. 